Prolactinoma

What do I have?

A prolactinoma is a benign tumor of the pituitary gland that produces too much of a normal hormone, prolactin. Prolactin is important for normal production of breast milk in women who are nursing, but otherwise it is present at low levels in both men and non-pregnant or non-nursing women. For reasons that are not well understood, prolactinomas are the most common pituitary tumor producing a hormone.

What does it do?

When a prolactinoma causes excess production of prolactin hormone, it can have different effects in men and women, and for women the effects depend on whether the woman is pre-menopausal or post-menopausal.

In pre-menopausal women, the elevated levels of prolactin are usually detected early because pre-menopausal women are very sensitive to the effects of prolactin. Women may start producing breast milk abnormally, or have breast enlargement and tenderness even though they are not pregnant. In others, menstrual periods may become irregular or stop completely, and infertility is common. After menopause, women are no longer as sensitive to the effects of prolactin and as a consequence the tumor will typically present when it has grown large enough to cause compression of the normal pituitary gland which may stop functioning properly. This usually leads to loss of normal hormone function, manifesting with hypothyroidism (fatigue, constipation, muscle pain, depression, cold intolerance, weight gain) or in extreme causes low cortisol which can be life-threatening, with symptoms such as low blood pressure, confusion, nausea, vomiting and fever.

If the tumor gets very large, it can cause pressure on the lining of the pituitary gland, leading to headache, or it can cause compression of the other nerves near the pituitary gland, especially the optic nerves that connect the eyes to the brain. This can lead to blurred vision or loss of peripheral vision.

In men, the most common symptom are due to low testosterone levels caused by prolactin leading to decreased libido, erectile dysfunction, and impotence; in some men, high prolactin levels and low testosterone levels will also cause breast enlargement and tenderness, but this is less common. In many cases, men will ignore these symptoms (sometimes because of embarrassment or because they believe they are “just getting older”), and the tumor will continue to enlarge until it causes the pituitary gland to be compressed further, leading to loss of normal hormone function, as discussed above. If the tumor gets very large, it can cause pressure on the lining of the pituitary gland, leading to headaches, or it can cause compression of other nerves near the pituitary gland, especially the optic nerves that connect the eyes to the brain. This can lead to blurred vision or loss of peripheral vision.

Many of these symptoms are not specific, meaning that people who have some of these symptoms may not have a prolactinoma, and many patients with a prolactinoma will only have some but not all of these symptoms. This is what makes diagnosis difficult. In addition, high levels of prolactin may be caused by a variety of other medical conditions as well as medications. This makes the diagnosis and management of prolactinomas very tricky, and requires expertise from both experienced endocrinologists and neurosurgeons.

How long have I had it?

Often the changes associated with these tumors are subtle, and they are typically slow growing, so it is likely that the tumor has been there for years before it was discovered, although pre-menopausal women typically develop symptoms much earlier because they are so sensitive to the effects of abnormally high prolactin levels in the blood. In addition, some patients have no symptoms at all from their tumor; in these cases, an MRI or CT scan was performed to help diagnose and treat an unrelated problem, and the tumor was discovered “incidentally”.

Can it be cured?

Unlike other pituitary tumors, most prolactinomas can be successfully treated medically, with either cabergoline (Dostinex®) or bromocriptine (Parlodel®). These drugs often reduce the size of the tumor and at the same time decrease the abnormally high level of prolactin in the blood very rapidly. Cabergoline or bromocriptine may control the tumor and bring the levels of prolactin in the blood back to normal, and they can make the tumor disappear especially if the tumor is very small. Treatment with these drugs may be continued for many years or indefinitely, but if the prolactin becomes normal or the tumor disappear these treatments can be discontinued with evidence of cure in about half of the patients treated.

In some cases, when patients have side effects from the medications, have other medical conditions that make it dangerous or difficult to take the medications, or have other reasons for not taking the medications, surgery is a safe and effective option. However, unless there are very good reasons to avoid medical treatment, we almost always recommend medical treatment as the first line for dealing with a prolactinoma.

What caused it?

For the majority of pituitary tumors, there is no known cause. These tumors appear to develop in a surprising number of patients without any clear reason. Recent work has suggested that there may be certain changes in the DNA of these tumors that lead to their formation, but their true cause remains elusive and is an active area of research.

In rare cases, these tumors may be part of a syndrome that can be inherited in families. For that reason, if anyone else in your family has ever had kidney stones, or has ever had a pituitary tumor, or has had any tumor of other hormone-producing organs (like the thyroid gland, the parathyroid gland, the kidneys, the adrenal glands, the pancreas, or the reproductive organs), let us know so that we can determine if your family is potentially a carrier for this inheritance.